1. Field of the Invention
The present invention relates to a drying machine and more specifically, to a power-saving drying machine control method, which uses auto control and electromechanical integration techniques and the characteristics of humidity in air to automatically shut off the drying machine in suitable time in order to obtain power consumption saving of the drying machine.
2. Description of the Related Art
Following prosperity of the society, laundry dryer has become one of the requisite electric home appliances. Many salary men, office ladies, or students are living in rented houses that do not provide a drying machine or drying yard for drying clothes. Therefore, laundry stores are opened in everywhere to meet the needs. However, most students cannot afford the high cleaning cost of laundry stores. Laundromats are then created in every corner of big cities around the world. These Laundromats use coin-operated washing machines and dryers for washing and drying laundry clothes. There are many motels providing coin-operated washing machines and dryer. In order to keep a clean outer appearance and to prevent falling accidents, many high-class apartments and mansions do not provide clotheslines or outdoor equipments for drying clothes, and thus residents shall have to use an electric drying machine to dry laundry clothes. The only drawback of a laundry dryer is its high consumption of power supply. However, a laundry dryer is conveniently to use and can prevent wrinkling of the clothes as well. In cities, more and more people use a laundry dryer to dry laundry clothes.
Further, in order to prevent contamination or for convenience and safety's sake, medicine and chemical suppliers commonly use an especial electric drying machine to dry medicines and chemicals.
According to the principle of design for conventional drying machines, air is sucked into the drying machine and heated by an electric heater into a dry air of medium high temperature and low relative humidity to dry laundry clothes (or materials) in a rotary drum that is being rotated by a motor, enabling water to be evaporated from the laundry clothes (or materials) into the air inside the rotary drum, thus the dry air with medium high temperature and low relative humidity is wetted and resulted in lowering its temperature and increasing its relative humidity, and the wet air is then expelled to the outside of the drying machine by means of a pressure difference. This procedure keeps running to make the laundry clothes be well dried. Conventional drying machines commonly use a timer to control the operation. When the set time is up, the time-control system will automatically shut off the machine. The user has to estimate the set time. In actual practice, it needs less time to dry same amount of laundry clothes (or materials) in dry weather than in wet weather. Further, it requires much more time to dry laundry clothes (or materials) that have strong absorptive power than laundry clothes (or materials) that are not absorptive. Therefore, it requires different drying time to dry different kinds and amounts of laundry clothes (or materials) during different ambient temperature or relative humidity. Even an experienced housekeeper (or drying machine technician) cannot accurately judge the drying time for every drying work. If the drying time is set too long, the laundry clothes (or materials) may be overheated, thereby wasting time and energy and causing damage to laundry clothes (or materials). If the drying time is set too short, the laundry clothes (or materials) will not be well dried, and the user shall have to set the timer to dry the laundry clothes (or materials) again. Further, a drying machine is an energy-consumptive device. At present, energy sources are getting short. Therefore, it is the common object of all countries around the world to save energy consumption while making the living comfortable.
Various drying machines and related control methods have been disclosed. According to UK Patent No. 1,470,163, temperature sensors are provided to detect the temperature of air passing through the electric heater and the temperature of air passing out of the drying machine, and the drying machine is shut 5 off when the temperature difference between the two temperature values from the two temperature sensors reaches a predetermined value. According to our tests, the temperature and relative humidity of the weather and the kind and weight of the laundry clothes affect the value of the temperature difference. Therefore, there is no reliable predetermined value shows a specific relationship with the dryness of the laundry clothes. If the predetermined value is set too low, the laundry clothes may be not well dried due to the conditions of low temperature and/or high relative humidity and/or laundry clothes' high water-retaining ability and/or laundry clothes' heavy weight. If the predetermined value is set too high, much energy and time will be wasted due to the conditions of high temperature and/or low relative humidity and/or laundry clothes' low water-retaining ability and/or laundry clothes' light weight. Therefore, this drying machine control method has limited accuracy for commercial application.
U.S. Pat. No. 4,485,566 discloses tumble dryer for the drying of laundry comprises a drum (2) arranged in a housing (1) and driven by a motor (3), heating means (7) for heating the air entering the dryer and being guided through the drum (2), first and second temperature sensing means (12, 13) for sensing the temperatures of the air led into the drum (2) and being discharged from the drum (2), and control means connected to the temperature sensing means (12, 13) for energizing and de-energizing the heating means (7) and the drum motor (3). In order to ensure a cooling down period dependent on the drum content and humidity to achieve a desired remaining humidity of the drum content the air led to the drum is guided for preheating before passing the heating means over and around the drum (2), the first temperature sensing means (12) is arranged for sensing the temperature of the preheated air (10) upstream of the heating means (7) and the control means de-energizes the heating means (7) upon reaching a first presettable temperature difference of the preheated and the discharged air (10, 8) and de-energizes the drum motor (3) upon reaching a second temperature difference of the preheated and the discharged air (10, 8).
According to the control method of U.S. Pat. No. 4,485,566, the temperature(T)-time(t) curve of the preheated air (10) obtained through the first temperature sensing means (12) is estimated to be curve K1 in FIG. 2, and the temperature(T)-time(t) curve of the discharged air (8) obtained through the second temperature sensing means (13) is estimated to be curve K3 in FIG. 2 (curve K2 in FIG. 2 is temperature(T)-time(t) curve of another design which is not described in detail by way of example, therefore no further discussion is necessary in this regard), wherein 0<t<t1 is the laundry clothes drying process; t1<t<t2 is the anti-wrinkling process to rapidly cool down the laundry clothes. According to this control method, the laundry clothes is regarded well dried when the temperature difference between K3 and K1 in FIG. 2 reaches a predetermined value, i.e., t−t1, and the central control unit cuts off power supply from the electric heater, keeping the fan and the drum motor in operation to run the anti-wrinkling process. However, curve K3 and curve K1 intersects when t=t2. This does not appear consistent with Second Law of Thermodynamics. Because curve K3 is a high temperature curve, and curve K1 is a temperature curve heated by high temperature curve K3, the temperature difference between curve K3 and curve K1 will always be greater than zero, and temperature difference between curve K3 and curve K1 will be equal to zero only when the time is infinity. Therefore, curve K3 and curve K1 are misleading temperature-time curves. Further, with respect to anti-wrinkling process, when the temperature difference between curve K3 and curve K1 is reduced to about the predetermined positive/negative value, i.e., at the time t=t2, it means the clothes (or materials) has been cooled down to a certain extent, and the central control unit will switch off the main power to shut down the machine. However, this design may encounter the problem that anti-wrinkling process is incomplete due to that the predetermined positive the temperature difference value is excessively high and the controlled time t2 is too short, or the motor is excessively operated to waste much energy and time due to that the predetermined positive temperature difference value is excessively low and the controlled time t2 is too long.
According to our tests, the temperature and relative humidity of the air outside the drying machine and the types and weight of the laundry clothes affect the value of the temperature difference between curves K3 and K1. Therefore, there is no reliable predetermined value shows a specific relationship with the dryness of the laundry clothes. If the predetermined value is set too low, the laundry clothes may be not well dried due to the conditions of low temperature and/or high relative humidity and/or laundry clothes' high water-retaining ability and/or laundry clothes' heavy weight. If the predetermined value is set too high, much energy and controlled time will be wasted due to the conditions of high temperature and/or low relative humidity and/or laundry clothes' low water-retaining ability and/or laundry clothes' light weight. If the predetermined value for the temperature difference between curve K3 and curve K1 in FIG. 4 is set too high and higher than the maximum temperature difference under the weather condition and the clothes' type and weight while the drying machine is operating, the temperature difference between curve K3 and curve K1 may never reach and the drying machine may never cut off power supply to the electric heater automatically. Therefore, the aforesaid two control have limitations in actual practice. More particularly, the method of automatically cutting off power supply to the electric heater imparts a difficulty in commercialization of this design.